This invention relates to optical fibre cables and in particular to the manufacture thereof and to joints between two elements thereof during manufacture or cable/cable joints.
In a design of optical fibre cable which is particularly but not exclusively suitable for submarine use and which is shown in section in FIG. 1 of the accompanying drawings, there is employed a central optical fibre package. The package includes a package strength member 1 made of high tensile steel wire which may if desired be copper plated to improve the electrical conductivity and which is coated with a plastics coating 2. Around the package strength member 1 are eight single mode secondary coated optical fibres 3 which are held in place by a fibre package whipping 4, such as a Kevlar ribbon. The fibre package is loosely housed in tubular member 5, which may be of aluminium and formed by closing an open aluminium "C"-section around the fibre package such that the edges of the "C"-section abut at 8. The tubular member 5 comprises a pressure resistant tube and may be employed for the transmission of electrical power or signals along the length of the cable. The optical fibre package and the annular gap 6 between the package and the inner wall of tubular member 5 may be impregnated and filled, respectively, with a water-blocking compound. Around the core are applied two layers of high tensile strength elements 9 and 10 which are torsionally balanced and applied with opposite lay directions. The outer layer 10 has more wires than the inner layer; the outer layer wires being smaller in diameter than the inner layer wires. For submarine cables there is extruded around the outside of and directly onto outer layer 10 a polyethylene dielectric sheath 11, and one or more armouring layers 12 may be applied over sheath 11.
For the manufacture of very long lengths, in particular of such optical fibre cable it is desirable to be able to joint two cable elements comprising the optical fibre package, the tubular member 5 and the strength member layers 9 and 10 before dielectric extrusion, in such a manner that the joint will subsequently pass through the dielectric extruder without difficulty, so that dielectric which is continuous and presents the same external diameter over all cable elements and joints therebetween may be obtained. Joints between two completed armoured or lightweight (unarmoured) fibre optic submarine cables must also be made in order to provide required cable lengths or mend damaged cables. At all of such joints the pressure resistant tubes 5 must be jointed in such a way that the tube is made effectively continuous over the length of the cable. In addition the strength members must be jointed in such a way that the loads applied to the strength members will be transmitted over the joint without causing damage to the cable members thereunder, in particular without causing stretching of the pressure-resistant tube 5 and subsequent stretching and possible fracture of the optical fibres therein. One known method of achieving jointing of the tube and the strength members is to employ a ferrule arrangement as disclosed, for example, in our U.K. application No. 39146/78, corresponding to U.S. Pat. No. 4,348,076 (R. C. Oldham--14). However, this particular ferrule arrangement, which was developed with an alternative cable construction in mind, is a relatively complex structure and results in a larger diameter over the joint region, with the result that the joint will not readily pass through a dielectric extruder unless it employs a variable-size extruder point as disclosed in our U.K. Application No. 8206374 corresponding to U.K. patent application No. 2,116,901 (M. P. Jones--1).
During the manufacture of optical fibre cable it may also be necessary to repair the tubular member 5 itself before the manufacturing process in which the strength member layers 9 and 10 are applied over it.